Vacuum extractors have long been used as a tool to assist delivery, primarily in vaginal deliveries. These extractors are often used when spontaneous vaginal delivery is not possible or is unsuccessful. They typically employ a bell shaped vacuum cup connected to a handle that is used to apply a tractive force to the cup with a tube being connected by an elongated stem. A manually or electrically powered suction device is attached to the cup either through a peripherally located vacuum port or through the stem.
In use, the surgeon attaches the open end of the vacuum cup over the fetal head. A vacuum is then drawn in the cup either through use of a manually operated vacuum pump or an electrical vacuum pump. The physician then pulls on the handle to apply a delivering force to the fetal head. The force applied to the extractor must be limited to prevent harm to the fetus. With conventional vacuum extractors reliance is placed on the physician's estimate of the force being applied to avoid the imposition of excessive forces.
It has been proposed to provide vacuum extractors incorporating sensors which measure the force applied between the vacuum cup and the handle to provide the physician with an indication of when excessive forces are being applied.
U.S. Pat. No. 6,355,047 discloses an extractor incorporating such a sensor and provides a slipping mechanism which causes the length of the force center to increase when an applied traction force exceeds a predetermined level. The physician may then use his judgment as to whether to continue to apply a greater force or to terminate use of the vacuum extractor. However, in some situations excessive force has been applied despite the incorporation of a force sensor and/or a slipping mechanism, resulting in the breaking of blood vessels connecting the fetal scalp from its underlying surface.